We provide a comprehensive assessment of the margins along which unions impact workers’ careers. To perform our analysis, we combine exogenous variation in union membership take-up with detailed administrative data and a novel field survey. In the survey, we investigate worker preferences over career amenities and their beliefs about the ability of unions to alter those amenities. In the administrative data, we causally estimate the channels through which unions influence worker outcomes, whether unions influence workers differently across their careers, and the overall longer-run effects of union membership. We find that the career effect of union membership differs greatly depending on the age at which workers enroll. In addition, we show that focusing on a restricted set of outcomes, such as wages and employment, generates a fractionalized understanding of the multidimensional career effect that union membership has on workers.